| TROPICAL STORM OHO DISCUSSION NUMBER 2 NWS CENTRAL PACIFIC HURRICANE CENTER HONOLULU HI CP072015 500 AM HST SAT OCT 03 2015 SATELLITE IMAGERY SHOWS THAT THE CYCLONE CONTINUES TO ORGANIZE... WITH A CURVED BAND OF DEEP CONVECTION WRAPPING INTO THE CENTER FROM THE SOUTH AND SOUTHEAST...WHILE COLD CLOUD TOPS HAVE PERSISTED NEAR THE CENTER. DVORAK INTENSITY ESTIMATES YIELDED DATA-T VALUES OF 2.5/35 KT...BUT WITH CONSTRAINTS...THE FINAL-T VALUES WERE LIMITED TO 2.0/30 KT. GIVEN THAT THE PATTERN-T ALSO SUPPORTS 2.5...AND THE PERSISTENCE OF THE STRONG CONVECTION OVER THE CENTER...THE INITIAL INTENSITY FOR THIS ADVISORY HAS BEEN INCREASED TO 35 KT...AND THE THE SYSTEM IS UPGRADED TO TROPICAL STORM OHO. THE INITIAL MOTION FOR THIS ADVISORY IS 360/05 KT. THE STORM IS EMBEDDED IN AN ENVIRONMENT CHARACTERIZED BY DEEP BUT RELATIVELY LIGHT SOUTHERLY FLOW BETWEEN A RIDGE ALOFT TO THE EAST AND A LARGE LONG WAVE TROUGH AND CLOSED LOW ALOFT TO THE NORTH. WHILE THIS GENERAL MOTION IS FORECAST TO CONTINUE IN THE SHORT-TERM...STEERING PATTERNS WILL BE RATHER DYNAMIC THROUGH THE FORECAST PERIOD...AND HAVE RESULTED IN A FORECAST TRACK BEST DESCRIBED AS RESEMBLING AN S...ESPECIALLY WHEN CONSIDERING PAST POSITIONS. THIS ARISES AS THE CYCLONE IS FORECAST TO MOVE NORTH...THEN WEST-NORTHWEST...WITH A FAIRLY SHARP TURN TOWARD THE EAST-NORTHEAST IN THE LATER FORECAST PERIODS. OVER THE NEXT 36 HOURS...THE LOW ALOFT TO THE DISTANT NORTH WILL LIFT QUICKLY NORTHWARD. THIS WILL ALLOW AN EAST PACIFIC MID- LEVEL RIDGE TO BUILD TO THE NORTH OF THE SYSTEM...THEREBY IMPARTING A MOTION TOWARD THE WEST-NORTHWEST. A NEW AND VIGOROUS TROUGH ALOFT WILL DIG SOUTHWARD TO THE NORTHWEST OF THE CYCLONE BY MONDAY...THEREBY WEAKENING ALREADY WEAK STEERING CURRENTS...WITH THE CYCLONE MEANDERING TO THE SOUTH OF THE BIG ISLAND SUNDAY NIGHT AND MONDAY. AS THE NEW TROUGH DIGS FURTHER SOUTH MONDAY NIGHT AND TUESDAY... IT WILL STEER THE SYSTEM GENERALLY TOWARD THE EAST- NORTHEAST. THE COMPLEX FORECAST TRACK...WHICH CLOSELY FOLLOWS THE TVCN CONSENSUS...HINGES ON THE EVOLUTION OF A VARIETY OF SYNOPTIC SCALE FEATURES...AND CONTAINS A GREATER THAN NORMAL AMOUNT OF UNCERTAINTY. ALSO ADDING TO THE UNCERTAINTY IS THE DEVELOPMENT OF ANOTHER LOW TO THE SOUTHEAST OF OHO IN THE GFS...AND TO A LESSER EXTENT...THE ECMWF. INTERACTION BETWEEN OHO AND THIS POTENTIALLY SPURIOUS LOW IN THE LATER MODEL FORECASTS ADDS ANOTHER LAYER OF UNCERTAINTY. WHILE THE OFFICIAL FORECAST KEEPS OHO AWAY FROM THE ISLANDS...IT IS IMPORTANT NOT TO FOCUS TOO CLOSELY ON THE EXACT FORECAST TRACK. ALSO...IT IS TOO EARLY TO TALK ABOUT SPECIFIC WIND...RAIN OR SURF IMPACTS FROM OHO IN THE HAWAIIAN ISLANDS. WITH THE DEPRESSION FORECAST TO BE SLOW-MOVING OVER VERY WARM WATERS IN AN ENVIRONMENT CHARACTERIZED BY LIGHT SHEAR...SIGNIFICANT INTENSIFICATION IS EXPECTED. IN FACT...SHIPS RAPID INTENSITY GUIDANCE CONTINUES TO INDICATE A HIGH CHANCE OF RAPID INTENSIFICATION OVER THE NEXT 24 HOURS. THE OFFICIAL FORECAST IS A LITTLE LESS AGGRESSIVE...BUT ANTICIPATES THAT OHO WILL BECOME A HURRICANE BY MONDAY...IN LINE WITH THE IVCN CONSENSUS. INCREASING SHEAR AND GRADUALLY DIMINISHING WATER TEMPERATURES ALONG THE FORECAST TRACK IN THE LATER PERIODS ARE EXPECTED TO LIMIT THE INTENSIFICATION SEEN IN THE EARLIER PERIODS. THE 53RD WEATHER RECONNAISSANCE SQUADRON HAS BEEN TASKED TO FLY THIS SYSTEM IN SUPPORT OF CPHC OPERATIONS...AND INITIAL FLIGHTS INTO THE SYSTEM ARE PLANNED FOR SUNDAY EVENING AND MONDAY MORNING. THE G-IV AIRCRAFT IS ALSO HEADING BACK TO HAWAII TO FLY SYNOPTIC MISSIONS...WITH HIGH-ALTITUDE FLIGHTS PLANNED FOR SUNDAY AND MONDAY MORNINGS...IN ORDER FOR THE DATA TO BE UTILIZED BY AFTERNOON MODEL RUNS. FORECAST POSITIONS AND MAX WINDS INIT 03/1500Z 14.2N 154.6W 35 KT 40 MPH 12H 04/0000Z 14.6N 154.7W 40 KT 45 MPH 24H 04/1200Z 15.1N 155.3W 50 KT 60 MPH 36H 05/0000Z 15.6N 156.0W 55 KT 65 MPH 48H 05/1200Z 16.0N 155.7W 65 KT 75 MPH 72H 06/1200Z 16.4N 154.7W 70 KT 80 MPH 96H 07/1200Z 17.0N 153.0W 70 KT 80 MPH 120H 08/1200Z 19.0N 151.0W 70 KT 80 MPH $$ FORECASTER BIRCHARD |